Phy 2053 Announcements I
Exam 1 info
1.
„
„
Please get there at least 10 minutes early, and preferably 20 minutes
H-ITT clicker grades:
5.
„
Up through and including gravitational potential energy – no springs!!
Room assignments
„
„
„
If your last name begins with A through P, you should go to Carleton
100
If your last name begins with R through Z, you should go to Pugh 170
You be allowed one handwritten formula sheet (both sides), 8 ½” x
11” paper
„
In class review, Tuesday, Feb 17
„
2.
Reitze will have special office hours Monday Feb 16 10 am 12 pm
4.
Material from sections 1.1 – 5.3 of Serway/Vuille, 20 questions,
multiple choice
„
Chan back in town next week; normal office hours
3.
Feb 18, 8:20 – 10:10 pm
„
Phy 2053 Announcements II
You may not receive any clicker grades this week; if not, don’t
worry, your grades are still being recorded and they will resume
when Prof. Chan returns
HW set #5 is not due until Feb 25
6.
„
Note: Exam 1 may include material that is covered in the HW
set (problems 5.28, 5,40, 5.78, 5.80, 5.85, and 5.92), so you
are strongly encouraged to complete this set before Exam 1
next week.
Professor Biswas at the helm today
Power
„
Example #5-53
The rate at which energy transfer takes place
Work F Δx
P =
=
= Fv
Δt
Δt
J
kg m 2
=1 3
s
s
„
SI units are Watts: 1 W =
„
Motors (US): 1 hp = 550 ft lb = 746 W
1
The electric motor of a model train accelerates the train from
rest to 0.620 m/s in 21 ms. The total mass of the train is 875 g.
Find the average power delivered to the train during the
acceleration. (Assume the train is on a level track.)
s
„
KW-h is a unit of energy (check your electric
bill!)
http://www.poormansmodelrailroad.com/sites/cjackson/_files/Image/jflayoutlrg.jpg
Center of Mass
(Center of Gravity near Earth’s Surface)
„
The point in the body which is used to measure the
change in gravitational potential
Try this at home
1
Why was energy a good concept to learn?
From Schroedinger equation
Because it was conserved.
Conservation of energy equation
in quantum mechanics
Physicists love conservation
(KE + PE) is conserved. PE is electrostatic (PHY2054)
KE =
Chapter 6
Momentum and Collisions
„
Momentum
„
The linear momentum of an object
of mass m moving with a velocity is
defined as the product of the mass
and the velocity
„
„
„
SI Units are kg m / s
Vector quantity, the direction of the
momentum is the same as the velocity’s
„
In order to change the momentum of an
object, a force must be applied
The time rate of change of momentum of an
object is equal to the net force acting on it
„
Gives an alternative statement of Newton’s second
law
r
Δp m(vf − v i ) r
=
= Fnet
Δt
Δt
p
t
2
Impulse
„
Average Force in Impulse
When a single, constant force acts
on the object, there is an impulse
delivered
to the object
r
r r
„ I = Δp = FΔt
„
„
is defined as the impulse
Vector quantity, the direction is the same
as the direction of the force
„
The average force
can be thought of as
the constant force
that would give the
same impulse to the
object in the time
interval as the actual
time-varying force
gives in the interval
r
r r
I = Δp = Fav Δt
Impulse-Momentum
Theorem
„
Where does it show up?
The theorem states that the impulse
acting on the object is equal to the
change in momentum of the object
„
r
I =
for a
constant force
„
If the force is not constant, use the
average force applied
If Δp is constant, increasing Δt will reduce Fav
and vice versa
r
r r
I = Δp = Fav Δt
Deliberately increasing
Δt to reduce Fav
Large Fav,
Small Δt
3
Good luck on your exam!!!
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